1. Field of the Invention
This invention relates generally to synchronization/back-up server systems, and more, specifically, to a method for multi-tier synchronization.
2. Description of the Background Art
Real-time synchronization systems, including client-server solutions such as MICROSOFT EXCHANGE (email/PIM) and SHARPCAST's first photo synchronization system, only synchronize data between a client and a server, where the client communicates with the server via the Internet. The advantage of client/server synchronization over the Internet is that the client device can access the server anytime it has an Internet connection. Also, by storing files on the server, the files can be easily recovered should the files on the client device be lost. There are at least two disadvantages with client/server synchronization over the Internet. Transferring files over the Internet is slower than transferring files over a local area network or an Intranet. Also, if a master server stores all synchronized files from many client devices, the master server has to have very large storage capabilities, which can be quite expensive.
An example of master server-client synchronization is described in U.S. patent application Ser. No. 11/269,498 titled “Method and Apparatus for a File Sharing and Synchronization System,” and filed on Nov. 8, 2005 with first-named inventor Jack B. Strong, the contents of which are incorporated by reference as if fully disclosed herein.
Known multi-tier data management systems, such as web proxies, content delivery networks, or file replication technologies, such as “rsync,” distribute file storage over the network. This means that client devices can retrieve files from intermediate sources instead of downloading then from a master server. Such intermediate sources may be connected to client devices over a local area network, where file transfers typically occur at a faster rate that transfers over the Internet. A disadvantage with known multi-tier data management systems is that data is not synchronized in real-time, which comprises user experience.
It would be desirable to have a synchronization system that was able to take advantage of the best of both multi-tier data management and client-server synchronization.